A wide variety of applications, such as signal analysis, signal processing, spectroscopy and others, are enabled by the use of an appropriate light absorbing material, commonly known as a spatially and spectrally selective holographic (SSH or S2) material or an inhomogeneously broadened transition (IBT) material. The material can be used in a variety of useful modes. In many applications, the SSH material is used to record a target analog spectrum in the frequency domain for the signal or signals of interest (SOIs) to be processed. The spectrum of one or more signals is made to interact with the SSH material by having them be modulated onto an optical laser carrier such that the modulated optical spectrum is resonant with the atomic absorbers in the SSH material. A modulated optical spectrum can represent either inherent optical information or radio frequency/microwave, millimeter wave information that is purposely imposed by modulating onto an optical laser carrier with an electro-optical modulator. The analog spectrum can be phase-sensitive in certain applications and conditions. Combinations of phase-sensitive analog spectra (e.g., multiplications) can result in correlative signal processing, data storage, or signal processing (e.g., see U.S. Pat. Nos. 7,265,712, and 7,307,781 and 7,471,224, the entire contents of each of which are hereby incorporated by references as if fully set forth herein).